IN THIS NEWSLETTER:
One of the most striking aspects of the changes occurring in veterinary medicine, is the increase in awareness by us, as veterinarians, and by the public of the need for postoperative pain management in animals. Whereas five or six years ago, only 50% to 60% of our clients opted for postoperative pain medication to go home with their pet, today we see close to 100% of our clients electing to have pain medication sent home. In many cases, we no longer offer them the option and routinely dispense appropriate pain medication at discharge.
The most frequently dispensed pain medications in our practice for postoperative pain control are the NSAID’s, or Non-Steroidal Anti-inflammatory Drugs.
While most of us are very familiar with Rimadyl® and Etogesic®, newer classes of NSAID’s are now available, and more are soon to follow as pharmaceutical companies develop more specific analgesics and anti-inflammatory agents with fewer side effects on non-targeted organs and tissues. The latest release to be FDA approved for use in animals is Deramaxx® (deracoxib) from Novartis.
Deramaxx® is touted as a coxib class drug, meaning it is specific for the inhibition of the Cox-2 enzyme, a potent precursor of inflammatory mediators. It uniquely inhibits the Cox-2 enzyme, while sparing (relatively) the Cox-1enzyme necessary for basal prostaglandin production and necessary for normal function of the g.i. tract, kidney, and platelets among others.
All of the terminology associated with these new drugs can be confusing and somewhat misleading. Terms such as “non-selective”, “preferential”, “selective”, “highly selective” and “specific” are often used to describe the newer NSAID’s which show increased selectivity for Cox-2 inhibition over Cox-1 inhibition. A better term for our understanding of these agents is probably to say they are “Cox-1 Sparing”. All NSAID’s act on the Cox-2 enzyme, that is how they mediate inflammation in tissues! By sparing the Cox-1 enzyme, however, the incidence of undesirable and potentially adverse side effects is lowered.
The most commonly used NSAID in our practice at this time is Rimadyl® at a dose of 2 mg/lb daily. The daily dose can be given once a day, or divided into two equal doses (1 mg/lb BID). I routinely recommend BID dosing, as the SID dose schedule has only recently been suggested by the manufacturer and we do not have enough cases using it to assess for efficacy over a 24 hour period with SID dosing. Etogesic® is recommended for SID administration, but has not had a significant duration of effect in my experience. We have recently begun using Deramaxx®, at a dose of 1.4 - 1.8 mg/lb (3-4 mg/kg) SID and initial results are promising in the postoperative orthopedic cases we have discharged with Deramaxx® for pain control. The manufacturer recommends it not be used for longer than 7 days in a row. It should also not be given with other anti-inflammatory drugs, especially NSAID’s or corticosteroids and it is better absorbed when given with food.
New drugs in development will include more specific targeting of the
Cox-2 enzyme and better sparing of the Cox-1 enzyme, and drugs which target
both cyclooxygenase and lipoxygenase inflammatory pathways. I am
also told that an injectable formulation of Rimadyl® should be available
sometime after the first of the year.
A primary goal of internal fixation of fractures is stabilization of the fracture with an early return to function. Intramedullary (IM) pinning is the most common form of internal fracture fixation utilized to achieve this. Properly applied, the IM pin should fill at least 75% of the medullary cavity in order to achieve its greatest stabilizing effect. Because of the curvature in various long bones, and variation in medullary canal size, achieving adequate fixation of fractures using a single IM pin is frequently impossible. The use of multiple IM pins , in an effort to increase stability by increasing the area of contact between the pins and bone, is termed Stack-Pinning.
There are five basic forces acting upon fractures. These include bending, rotation, shear, compression and distraction. Determination of the force, or frequently forces, acting upon each fracture helps us plan the surgical technique most likely to neutralize these forces and achieve fracture healing. Single IM pins are effective in counteracting primarily bending forces. Unless the medullary canal is filled completely by the pin, the other forces acting upon the fracture are not counteracted. The use of stack-pinning allows for neutralization of bending forces as well as shear and rotational forces, by achieving multiple points of contact with the cortex and multiple sites of fixation in the proximal and distal metaphyses.
Stack-pinning is particularly suited for transverse, as well as short oblique fractures of the middle humerus and femur. When used in conjunction with another form of fixation such as cerclage or hemicerclage wires, stack pinning may also be suitable for long oblique and comminuted fractures of the humerus and femur.
Specific techniques of application and insertion are detailed in surgical texts. The interested reader is urged to consult these for more detail.
Few complications are associated with proper use of stack-pinning in fracture repairs. Failure to identify fissures in the cortex of the bone may lead to splitting of the cortex as the medullary canal is filled with pins. Fissures should be identified prior to insertion of pins and stabilized with the appropriate use of cerclage wires. Failure to stabilize fissures, or an inability to stabilize fissures, may dictate a change to an alternative method of fixation.
After retrograde insertion of pins into the proximal fracture fragment, it may be difficult to drive pins into the distal segment with a hand chuck because of the close proximity of the multiple pin ends. Power insertion of the pins using a low-speed drill, or seating pins with a mallet, may be necessary. Alternatively, the first pin may be placed in retrograde fashion out the proximal fragment, the fracture reduced, and the pin then seated in the distal fragment. Subsequent pins are inserted normograde from the crest of the greater tubercle in the humerus, or the greater trochanter and trochanteric fossa of the femur. This reduction technique works especially well in the femur, where pins tend to converge in the trochanteric fossa when all are inserted in retrograde fashion.
Pin migration may be a problem, particularly if the pin or pins are
not seated firmly in the distal metaphysis. The use of partially
threaded IM pins, seating the threaded portion in the metaphysis, is beneficial
in minimizing migration. If the pin or pins do migrate out, it should
be removed and an ancillary method of fixation applied such as a Kirschner-Ehmer
apparatus. Re-insertion of the pin is usually unsuccessful and not recommended.
One of the most common forelimb fractures in miniature- and toy-breed dogs is a fracture of the distal radius and ulna. This may be the fracture with the most common risk of non-union, and the high incidence of complications makes this fracture a management challenge for the veterinarian.
Fracture Location and Risk for Complications
Fracture of the distal radius and ulna occurs most commonly in the distal 1/3 to 1/4 of the bone, many times after relatively minor trauma. A common scenario described by the owner is a jump or fall from a relatively minor height, resulting in sudden lameness attributable to fracture. In most instances, the fracture is a relatively clean, transverse or short oblique fracture which is inherently unstable.
Complications from these fractures have been detailed in numerous articles and veterinary texts. In one study, fractures of the distal radius and ulna accounted for 12 of 47 (44%) non-unions whereas in another study, they accounted for 40%. In that study 85% of fractures managed with cast or IM pin fixation in dogs greater than one year of age failed to heal.
Cast fixation and intramedullary (IM) pinning were considered unacceptable methods of fixation for small dogs in that study, because 83% developed serious complications. in that same series, plate fixation resulted in favorable outcomes in over 80% of small dogs.
Salvage of failed fixation may not be possible in all cases. In another study, 23% of small dogs with complications from radial and ulnar fractures eventually underwent limb amputation.
Cast fixation or the use of intramedullary pinning alone is considered a poor option and is not recommended. The risk of complications and the high incidence of complications should be explained to the client if this option is selected for financial or other reasons, and documentation of that discussion should be noted in the patient's record. Anatomical alignment is difficult to achieve with cast fixation, and reduction is easily lost with the slight motion that invariably occurs under the cast, and as soft tissue swelling subsides under the cast. Intramedullary pinning may lead to non-union or radiocarpal joint dysfunction. These are usually clean fractures which do not interdigitate well, and an IM pin alone does not stabilize adequately against rotational forces. In addition, the medullary canal is small and the pin utilized must be comparatively small in relation to the size of the bone; bending forces may also be inadequately neutralized with an IM pin. An IM pin may destroy the medullary blood supply to the bone.
Optimum fixation involves neutralization of all forces acting upon the
fracture combined with accurate, anatomical reduction and preservation
of blood supply tot he bone. The best method for achieving consistent and
predictable healing of these fractures is open reduction and stabilization
using either a bone plate or an external fixator. Both methods have inherent
advantages and disadvantages including the availability of bone distal
to the fracture in which to place implants and the small size of the bone,
as well as the equipment, materials and technical skill needed to properly
apply either of the above methods. A bone plate provides excellent, rigid
internal fixation and limited interference with function. There must be
sufficient bone distal to the fracture to place at least 2 screws in the
plate, which may preclude use of a bone plate. A disadvantage of plate
fixation is that stress protection can occur under a bone plate, resulting
in weakening of the bone. this makes removal of the plate optimum, however;
plate removal entails another surgical procedure and postoperative confinement
while the empty screw holes fill in with new bone. External fixation also
provides good fixation, and can be applied in numerous configurations to
achieve sufficient rigidity. An external fixator is readily removed, but
had inherent disadvantages in that it can be difficult to apply pins to
the radius and pin size, and thus the rigidity of the fixator, is limited
by the relatively small size of the bones. Premature pin loosening may
require re-application of the fixator.
Triple pelvic osteotomy (TPO) is a well established surgical technique for correction/alleviation of hip dysplasia in the dog. TPO has been done for many years, and there is good long-term follow-up available so that we can tell clients what to expect in the properly selected candidate. The advantage to the TPO procedure is that it preserves the natural coxofemoral joint of the patient by improving femoral head coverage within the acetabulum, creating a “tighter” fit to the hip joint and a more congruent joint surface.
While we are all familiar with hip dysplasia and the clinical and radiographic appearance of the dysplastic hip joint, TPO remains an under-utilized surgical procedure which has many benefits over alternative procedures such as the femoral head ostectomy and total hip joint replacement. For the TPO procedure to be optimally successful, proper patient selection is crucial and this requires us, as veterinarians, to recognize the early signs of dysplasia and to identify and screen patients at-risk early in the course of the disease.
For the triple pelvic osteotomy procedure to be successful, proper patient selection is crucial. The following factors are critical in obtaining a successful outcome:
Anatomy. The hip joint itself must be of relatively normal shape. Both the femoral head and the acetabulum must be normal, i.e. there should be no DJD noted and the shape of the femoral head should be normal (do not confuse the normal depression where the round ligament originates on the femoral head for an irregularity). The acetabulum should be of normal depth. The joint does not fit together properly - laxity is the primary abnormality. There is less than 50% coverage of the femoral head within the acetabulum. A triple pelvic osteotomy should not be done in the presence of DJD or with a very shallow acetabulum. Whether or not TPO can stop the progression of DJD in an arthritic hip, and at what point, is the subject of debate.
Age. The age of the patient is a consideration. Surgery cannot be done too early, as the bone is too soft to secure implants properly. Most surgeons consider the ideal patient to be between eight (8) and fourteen (14) months of age. Individual preference may lengthen that time frame, and I personally will extend that time frame based upon the circumstances of each case.
Owner and Patient. There is no point in doing a TPO if the owner is not going to adhere to postoperative instructions or if the patient is unmanageable and cannot be adequately confined during the postoperative healing. Uncontrolled activity may cause premature loosening of the implants and result in disastrous complications. It is imperative that postoperative confinement restrictions be discussed fully with each owner prior to doing the surgery.
Suspected hip dysplasia should be evaluated by a thorough physical and radiographic examination. The key is to evaluate the patient at a young age so that the TPO procedure can be considered. Patients at-risk or showing symptoms of dysplasia who are at least 6 months of age should be evaluated radiographically to see if they are a candidate for TPO. The client then must be educated about hip dysplasia as well as the surgical procedures available. A useful tool in explaining hip dysplasia and showing the client how dysplasia progresses over time, is a composite radiograph available through Slocum Enterprises, Inc. (phone 1-800-346-5489). This radiograph not only shows the dysplastic hip, it illustrates several surgical techniques including the triple pelvic osteotomy, femoral head and neck excision, and total hip replacement.
In summary, Triple Pelvic Osteotomy is an extremely useful surgical
procedure in the properly selected patient. If you would like additional
information on TPO’s, please do not hesitate to contact the office.